Known power semiconductors produce heat as a by-product. At the same time, in order for a power semiconductor to function, its temperature should be kept within a given range. As a result, power semiconductors should be cooled.
Power electronic devices may, for instance, be cooled by a two-phase cooling system. Such a two-phase cooling system may, for example, include a circulatory system where a coolant is transferred between an evaporator and a condenser.
The evaporator is thermally connected to a heat source, for example an IGBT module. In the evaporator, the coolant is evaporated. Evaporating the coolant ties down heat, and thereby cools the heat source. The evaporated coolant is then moved to the condenser by using the circulatory system. In the condenser, the coolant is condensed and the heat it contains is released. This heat can be transferred to a flow of air.
FIG. 1 illustrates a first two-phase cooling system in accordance with a prior art implementation. As shown in FIG. 1 an evaporator 10 is connected to a condenser made of a stack of panels 11 via coolant conduits 12. Power electronic devices, in this case IGBT modules 13, are mounted on the evaporator 10. FIG. 2 illustrates a second two-phase cooling system in accordance with a prior art implementation. As shown in FIG. 2, condenser panels 20 are embedded in a base plate 21, to which power electronic devices 22 are attached.
The flow of air may be gravitational or produced mechanically. An air flow generated by gravity has a limited air speed, which means a limited heat-transfer coefficient and, hence, a limited cooling performance. In order to achieve higher performance, a mechanically produced air flow may have to be used. A fan can be used to produce an air flow.
FIG. 3 shows a schematic diagram of an exemplary power drive system with an air ventilation system in accordance with a prior art implementation. The air ventilation system consists of an air duct 30 inside which a fan 31 is provided for generating the air flow, and a stack of condenser panels 32. The condenser panels 32 transfer heat from power electronic devices 33 mounted on an evaporator 34 to the air flow. A passive component 35, such as a choke, may also be placed in the air duct 30 to be cooled by the air flow.
In FIG. 3, the achievable cooling performance may be limited owing to acoustic noise restrictions. The fan 31 may constitute a dominant noise source, and the noise level may increase strongly along with an increasing air volume flow rate or speed, respectively. Noise generated by the fan 31 can propagate in the air of the duct 30, and through inlet and outlet, out of the duct into the environment, where the allowable noise level is limited.
The allowable noise level may limit the maximum air speed used, and a limited air speed, in turn, may limit a heat-transfer coefficient between the air flow and the panel, and hence limit the cooling performance.
To reduce the emission of air-borne noise into the environment in the power drive system of FIG. 3 (or, alternatively, to allow for an increase in fan and hence cooling power, while still respecting the noise limits), the air duct system 30 may be equipped with means for attenuating the noise. As the noise may propagate upstream and downstream from the fan 31, two additional components may be called for in the ventilation system. However, adding these components may increase the volume, weight, pressure drop and cost of the cooling arrangement.